1. Field of the Invention
The present invention relates to a motor for use in a blower or the like and, more particularly, to an improvement of a motor provided with a circuit board to which coils of a stator are connected.
2. Description of the Related Art
A centrifugal fan used as a blower for cooling electronic devices and so forth is configured such that, as a plurality of circumferentially-arranged blades is rotated by a motor about a rotation axis, axially-drawn air is radially discharged and then blown out from an exhaust port.
The centrifugal fan of this type generally has a configuration as disclosed in, e.g., Japanese Patent Application Publication No. 2005-256610. More specifically, an impeller including a ring-shaped hub extending radially outward from a rotor unit and a plurality of blades fixed to the hub and circumferentially arranged at the radial outer side of the rotor unit is fixed to the rotor unit having a substantially cylindrical portion rotating about a rotation shaft. A bearing unit for supporting the rotation shaft of the rotor unit is held inside of a bearing holder unit arranged in a base. A stator unit arranged on the inner circumference of the rotor unit is fixed to the outer surface of the bearing holder unit. A circuit board is arranged between the base and the stator unit.
In general, the circuit board is formed into a ring shape so as to be loosely fitted to the outer surface of the bearing holder unit. As disclosed in Japanese Patent Application Publication No. 2005-256610, tying pins implanted in an insulator of the stator unit are soldered to the circuit board, whereby the circuit board is supported on the stator unit. The coils of the stator unit are tied and connected to the tying pins. Thus, the coils are connected to the circuit board through the tying pins.
In the configuration in which the circuit board is supported by only the tying pins of the stator unit as set forth above, the circuit board tends to vibrate if the electromagnetic vibration generated in the stator unit is transferred to the circuit board. In addition, the circuit board may be vibrated when a part of the airflow generated by the rotation of the impeller flows around the circuit board. This may adversely affect the vibration and noise characteristics of the centrifugal fan as a whole.
A technology for solving the aforementioned problem is disclosed in, e.g., Japanese Patent Application Publication No. H07-075288. In Japanese Patent Application Publication No. H07-075288, a recess portion is formed in a counter intake port of a fan casing. A circuit board is arranged in the recess portion and is encapsulated with a resin sealant. With this structure, the circuit board is covered with the resin sealant and is fixed to the fan casing. It is therefore possible to obtain a vibration-free structure for the circuit board and to provide dustproof and waterproof effects.
In case of the configuration disclosed in Japanese Patent Application Publication No. H07-075288, however, the recess portion for the accommodation of the circuit board needs to be secured when encapsulating the circuit board with the sealant. If it is structurally impossible to provide the recess portion, a wall for covering the circuit board needs to be temporarily prepared in order to fill the sealant. This poses a problem in that the structure becomes complex. Moreover, a drying step needs to be performed after filling the sealant. Thus, there is a problem in that the number of required manufacturing steps grows larger and the installation becomes larger.